Manufacturing processes for automobiles have evolved from one that utilized primarily stamped and bent sheet metal pieces that were welded together through a MIG welding processes, i.e. a welding process in which a line of molten material is deposited by the welder in joining two pieces of metal together. Now, conventional automobile manufacturing processes incorporate in a greater degree hydroformed tubular members that are shaped to fit into the chassis of an automobile in a desired manner. The hydroformed members are particularly conducive to being welded through a spot-welding process, which involves the passage of electrical current between two electrodes to melt and join two pieces of metal placed between the electrodes. Spot-welding requires a frame design having appropriate access holes that is conducive to being manufactured using the spot-welding process. For example, if two tubular members are being spot-welded together, access to the adjoining walls of the two tubular members by the spot-welder electrodes must be provided. Other welding techniques, such as gas metal arc welding (GMAW), are also be utilized for welding tubular designs.
Roll-forming is a process for forming a structural tubular member involving the transformation of a piece of flat sheet metal into the structural beam by passing the sheet metal through a series of rollers arranged to bend the sheet metal into the structural beam. Generally, tubular members are formed through the roll-forming process. These tubular members can be used directly in the manufacture of an apparatus, such as an automobile, or be used in a subsequent manufacturing process called hydroforming to create a specially shaped and bent structural member that roll-forming cannot by itself create.
Hydroforming is a process by which a standard tubular stock member is placed into a form shaped to correspond to the particular member to be formed. A liquid is then introduced into the interior of the tubular stock and pressurized until the tubular stock expands to assume the shape defined by the configured form. The expanded and re-shaped tubular stock now has a substantially different shape. By forming cutouts and other access openings into the re-shaped tubular member, spot-welding electrodes can gain access to opposing adjacent sides to create a weld bond between juxtaposed members. In this manner, a frame, as an example, for an automobile can be created using in large part hydroformed tubular members. Once the hydroformed part is formed, attachment brackets are attached to the part to permit other components of the automobile to be mounted. Typically, these attachment brackets are welded to the hydroformed part by either a MIG or spot-welding process, whereupon the other components can then be bolted or welded to the attachment brackets.
Whether hydroformed or merely roll-formed, the structural tubular member is not conventionally formed with any internal reinforcement and, thus, the walls of the tubular member must carry the entire load placed on the structural member and provide the requisite stiffness needed for the structural member to perform its operative function. The load carrying ability of the tubular member is a limiting factor in the design of hydroformed or roll-formed structural members and can result in a non-optimized beam design having increased material thickness in the walls of the beam or increased tube diameter. Either of these enhanced load carrying characteristics leads to an expensive overweight design. Furthermore, the increasing of the tube diameter causes problems in the packaging of the enhanced design, making automotive design more difficult.
Accordingly, it would be desirable to provide a manufacturing process by which the structural beam can be formed with multiple tubular cells that provide a single structural member having an integral internal reinforcement to increase structural strength for a roll-formed beam of a given size and shape.